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In order to determine the self-diffusion coefficients D of all the species in the solutions at 298.2 K, 1H and 19F NMR diffusion ordered spectroscopy (DOSY) has been conducted on coumarin 153 (C153) in binary mixed solvents of an imidazolium-based ionic liquid (IL), 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (C12mimTFSA), with three molecular liquids (MLs) of chloroform (CL), benzene (BZ), and propylene carbonate (PC) as a function of ML mole fraction xML. Below xML ≈ 0.8, the D values of each species do not significantly depend on the MLs. However, above this mole fraction, the diffusion of C153 becomes smoother in the order of BZ ≈ CL > PC systems. The interactions among C153, C12mim+, TFSA−, and ML molecules have been investigated using infrared (IR) and 1H and 13C NMR spectroscopic techniques. The relations of the diffusion of the species with the interactions among them have been discussed on the molecular scale. In the IL solution, the C153 carbonyl oxygen atom is hydrogen-bonded with the imidazolium ring C2–H atom of C12mim+. C12mim+ also forms an ion pair with TFSA−. Thus, C153, C12mim+, and TFSA− cooperatively move in the CL and BZ solutions at a lower ML content, xML < ∼0.8. On the other hand, at a higher ML content, xML > ∼0.8, the C153 molecule diffuses with CL and BZ molecules because of the hydrogen bonding between the C153 carbonyl O atom and the CL H atom and the π–π interaction between the C153 and BZ ring planes, respectively. For the PC system, the change in the relative self-diffusion coefficients of each species with increasing xML differs from those for the CL and BZ systems because of both hydrogen bonding donor H and acceptor O atoms of PC for C153, the IL cation and anion, and PC themselves. [ABSTRACT FROM AUTHOR]

The upper critical solution temperature (UCST)-type liquid–liquid phase separation of imidazolium-based ionic liquids (ILs), 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Cnmim][TFSI], where n represents the alkyl chain length of the cation, n = 6, 8, 10, and 12) binary solutions with formamide (FA) was examined as a function of temperature and the FA mole fraction xFA. The two-phase region (immiscible region) of the solutions is much larger and expands more with the increase in n, in comparison with the previous [Cnmim][TFSI]–1,4-dioxane (1,4-DIO) systems. An array of spectroscopic techniques, including 1H and 13C NMR and IR combined with molecular dynamics (MD) simulations, was conducted on the present binary systems to clarify the microscopic interactions that contribute to the phase-separation mechanism. The hydrogen-bonding interactions of the imidazolium ring H atoms are more favorable with the O atoms of the FA molecules than with 1,4-DIO molecules, whereas the latter interact more favorably with the alkyl chain of the cation. Upon lowering the temperature, the FA molecules gradually self-aggregate through self-hydrogen bonding to form FA clusters. Concomitantly, clusters of ILs are formed via the electrostatic interaction between the counter ions and the dispersion force among the IL alkyl chains. Small-angle neutron scattering (SANS) experiments on the [C6mim][TFSI]–FA-d2 and [C8mim][TFSI]–FA-d2 systems revealed, similarly to [Cnmim][TFSI]–1,4-DIO systems, the crossover of the mechanism from the 3D-Ising mechanism around the UCST xFA to the mean-field mechanism at both sides of the mole fraction. Interestingly, the xFA range of the 3D-Ising mechanism for the FA systems is wider compared with the range of the 1,4-DIO systems. In this way, the self-hydrogen bonding among FA molecules most significantly governs the phase equilibria of the [Cnmim][TFSI]–FA systems. [ABSTRACT FROM AUTHOR]

The investigation of the structures of acetic acid (AA), trifluoroacetic acid (TFA), and their aqueous mixtures over the entire range of acid mole fraction [x.sub.A] by large-angle X-ray scattering (LAXS) has shown that acetic acid molecules mainly form a chain structure via hydrogen bonding in the pure liquid.

The structure of bis(trifluoromethanesulfonyl) imide(TFSI(super minus)) in the liquid state was studied by means of Raman spectroscopy and DFL Calculations. The results concluded that a conformational equilibrium was established between the C(sub 1) and C(sub 2) conformers of TFSI(super minus) in the liquid EMI(super plus)TFSI(super -) and the C2 conformer is more favorable than the C1 one.

Raman spectroscopy was used for obtaining the individual N,N-dimethylformamide (DMF) and protic N-methylformamide (NMF) solvation numbers of manganese (II), nickel (II) and zinc (II) ions. The metal ions were preferentially solvated by DMF at xDMF > 0.5 whereas no preferential solvation occurred in mixtures with DMF mole fraction of xDMF < 0.5.

The information about the structure of dimethyl sulfoxide (DMSO)-water mixtures at relatively low DMSO mole fractions is an important step in order to understand their cryoprotective properties as well as the solvation process of proteins and amino acids. Classical MD simulations, using the potential model combination that best reproduces the free energy of mixing of these compounds, are used to analyze the local structure of DMSO-water mixtures at DMSO mole fractions below 0.2. Significant changes in the local structure of DMSO are observed around the DMSO mole fraction of 0.1. The array of evidence, based on the cluster and the metric and topological parameters of the Voronoi polyhedra distributions, indicates that these changes are associated with the simultaneous increase of the number of DMSO-water and decrease of water-water hydrogen bonds with increasing DMSO concentration. The inversion between the dominance of these two types of H-bonds occurs around XDMSO = 0.1, above which the DMSO-DMSO interactions also start playing an important role. In other words, below the DMSO mole fraction of 0.1, DMSO molecules are mainly solvated by water molecules, while above it, their solvation shell consists of a mixture of water and DMSO. The trigonal, tetrahedral, and trigonal bipyramidal distributions of water shift to lower corresponding order parameter values indicating the loosening of these orientations. Adding DMSO does not affect the hydrogen bonding between a reference water molecule and its first neighbor hydrogen bonded water molecules, while it increases the bent hydrogen bond geometry involving the second ones. The close-packed local structure of the third, fourth, and fifth water neighbors also is reinforced. In accordance with previous theoretical and experimental data, the hydrogen bonding between water and the first, the second, and the third DMSO neighbors is stronger than that with its corresponding water neighbors. At a givenDMSOmole fraction, the behavior of the intensity of the high orientational order parameter values indicates that water molecules are more ordered in the vicinity of the hydrophilic group while their structure is close-packed near the hydrophobic group of DMSO. [ABSTRACT FROM AUTHOR]

Large-angle X-ray scattering (LAXS) measurements are made at 298 K on 2,2,2-trifluoroethanol (TFE), 2,2,2-trichloroethanol (TCE), and their aqueous mixtures to clarify the structure of solvent clusters formed in halogenoethanol-water mixtures at the molecular levels. The most likely structure models of solvent clusters predominantly formed in TFE-water and TCE-water mixtures are proposed.

The present large-angle X-ray scattering (LAXS) investigation on methanol confined in the MCM-41 C14 (diameter of 28 Angstrom) and C10 (21 Angstrom) pores has shown that the structure of methanol consists of the monolayer methanol on the surface and the hydrogen-bonded chains of methanol molecules at the central part of the pores. The methanol structure cannot be three-dimensionally evolved in the pores with decreasing temperature.